Oligobrachia

Oligobrachia is a genus in the family Siboglinidae,^[1] commonly known as beard worms. These beard worms are typically found at spreading centers, hydrothermal vents, and undersea volcanoes.^[2] The siboglinidae are annelids which can be found buried in sediments. Beard worms do not necessarily exist at one specific part of the world's oceans, however, they are spread out all over the ocean floors as long as the surrounding environment is similar; these are known as metapopulations.^[3] Most commonly, these organisms are found at the bottom of the ocean floor, whether it be at a depth of roughly 25 meters or hundreds of meters.^[4] Oligobrachia can typically be found near hydrothermal vents and methane seeps. An important characteristic of this genus is that it lacks a mouth and gut. Therefore, it relies on symbiotic bacteria to provide the host organism with energy to survive. The majority of oligobrachia that have been observed have been found in the Arctic and other high-latitude areas of the world's oceans.^[5]

Endosymbiotic bacteria

Oligobrachia or any genus within the siboglinidae family, lack a mouth or gut. Therefore, this family has evolved to develop a symbiotic relationship with bacteria.^[6] These symbionts provide up to half of the DNA for their tubeworm hosts. Additionally, these symbionts are shared amongst all species within a generation, known as horizontal transmission, as tubeworms reproduce. This is different from vertical transmission, which is the transmission of DNA from parents to offspring.^[7] This can serve as a costly evolutionary trait due to the fact that environments can change over time.^[8] Even hydrothermal vents, which are hypothesized to be some of the most stable environments on Earth, can go through changes that would alter the proportion of chemicals in the area. The oligobrachia genus has developed the evolutionary capability of having specialized cells that provide a habitat for the endosymbiotic bacteria that the tube worm relies on to survive. Depending on the habitat the oligobrachia lives near, whether it is a hydrothermal vent or an undersea volcano, the endosymbiotic bacteria will oxidize methane, sulfide, or what ever the dominant chemicals in the water are. Studies have found that oligobrachia are able to select for the type of endosymbiotic bacteria they will need in order to be best adapted to live in their environment. These bacteria can be either thioautotrophic (feeds on sulfide) or methanotrophic (feeds on methane).^[4] Oligobrachia that live near these undersea volcanoes will most likely select for thioautotrophic endosymbiotic bacteria, while oligobrachia that live near hydrothermal vents will most likely select for methanotrophic bacteria.

Hemoglobin production

There has been some studies that have explored the hemoglobin production of beard worms. It has since been found that the site of hemoglobin production is located in the peritoneal membrane in the posterior body.^[9] The minimal studies that explore this process within the tubeworm found that the site of hemoglobin production is the peritoneal membrane.^[9]

Internal anatomy

Out of the known deep sea organisms, tubeworms are some of the most widely studied. When it comes to the nervous system, the majority of studies that exist mostly pertain to the central nervous system, as opposed to the peripheral nervous system.^[10] Studies found that the sensory systems of tubeworms consist essentially of three main features: epidermal solitary sensory cells, sensory spots, and what are assumed to be sensory organs.^[10] The lack of diversity among the nervous systems of tubeworms that were studied were found to be a possible explanation for the origin of the genus, oligobrachia.^[10]

Development

Siboglinidae is one of the most studied genus out of the deep-sea marine organisms that are currently discovered. During the development of the tube worm, it has been found that they development the trophophore, with is the part of the body that hosts its endosymbiotic bacteria. It has been hypothesized that this part of the body is developed by the bacteria that rely on this feature of the tubeworm's internal anatomy in order to be able to carry out processes that siboglinidae cannot conduct on its own. As previously mentioned, siboglinidae lack a mouth or gut; endosymbiotic bacteria helps carry out these processes for the tubeworms in exchange for a place to live.^[11] Studies that exist regarding the development of oligobrachia have found this species incubating embryos.^[12]

References